1. Field of the Invention
The invention relates to a non-helical torsion spring system. Such a system may be used between a frame or chassis of a vehicle and a vehicle suspension member.
2. Description of the Related Art
True torsion springs or rods (non-helical or coil) are objects which twist the material of an object around the longitudinal axis of that object and as such are limited by the rapid onset of internal stresses created within the element. Those stresses restrict spring loading, range of rotation, usable spring arc, cycle life and spring efficiency, while creating deformations within the torsion element, inducing element failure and preventing composite or non-metallic construction.
Helical or coiled springs, such as those disclosed in U.S. Pat. Nos. 5,464,197 and 4,961,743, or garage door springs, where only a configuration or “coil shape” of the object is referenced to rotate with respect to another “coil shape” of the object, but the material between is flexing in simple tension and compression, is not a true torsion device. True torsion is a specific movement of objects wherein adjacent materials within the object are twisted in opposing directions.
The first three stresses of the true torsion element are significant obstacles because they increase by the square of the radius of the element and prevent the construction of efficient, wide load range, controllable torsion spring systems.
The first internal stress occurs as the center material of the element twists in a straight path while the outer material (displaced from the centerline) rotates in a longer spiral path and stresses lengthwise relative to the center. Two equal and opposite end points of an object at zero rotation, become equal and opposite end points again after 360 degrees of rotation but the intervening material between the two points has undergone considerable lengthwise stress compared to the center material because of its longer spiral path.
The second internal stress is also longitudinal shear but at right angles to the first. If one visualizes the element as a stack of drinking straws or small columns, as the ends rotate in opposite directions or in torsion, the straws or columns in the outer layer shift lengthwise in relation to each other. Torsion in either direction creates a series of lengthwise stresses between each column, and area of material. Each lengthwise segment of each layer or material of equal distance from the center is placed in shear stress with the adjacent material in the same or equal distance from the center layer.
The third internal stress is torsion's attempt to rotate each group of molecules or areas in torsion around their own centers and places the areas or zones between adjacent material groups in rotational stress. Those edge zones of adjacent material attempt to rotate in the same direction, like rolling pencils on a surface reveal similar rotations of the material, but which also demonstrates that the surfaces between those columns shear in opposite directions.
Those stresses increase by the square of the radius so that a doubling of the radius increases the stresses by a factor of four. Stresses are unavoidable in torsion because each particle or portion of the torsion element is in an unequal orbital arc or unequal three-dimensional motions compared to all other particles or portions of the element.
The forth stress is the conflict between torsion and flexion at the intersection between the torsion material and its fixed attachment ends. The material at the end of a torsion element is secured rigidly, even by a simple 90-degree hook attachment. At that narrow transverse junction, the rigidly fixed material abruptly flexes with the spiral angle formed by the material in torsion. That reversing angle change creates a focus of destructive tension in a narrow zone directly across and completely through the torsion material. That coincides with the most common fatigue fracture or failure point in torsion rods.
Devices having a single torsion bar are disclosed, for example, in U.S. Pat. Nos. 6,099,006, 6,431,531, 5,716,042 and 6,945,522. Bars which are hollow, have non-round cross sections or include multiple concentric pipes are disclosed, for example, in U.S. Pat. Nos. 5,556,083, 4,884,790 and 5,020,783. Devices having multiple rods are disclosed, for example, in U.S. Pat. Nos. 6,877,728, 5,158,321, 6,752,411 and 5,163,701. Devices with elastic mountings are disclosed, for example, in U.S. Pat. Nos. 5,382,007 and 4,966,386. U.S. Pat. No. 5,326,128 shows a device which is adjustable only by disassembly and replacement of parts. U.S. Pat. No. 6,454,284 shows a device which is adjustable only in portions. U.S. Pat. No. 6,241,224 teaches a torsion spring made of an elastic compound between plastic end pieces. All of those devices suffer from the stresses described above.